Copper alloy for slide fasteners having excellent continuous castability

ABSTRACT

The object of the present invention is to provide a copper alloy for slide fasteners which has excellent whiteness, does not contain nickel and hence does not have the problem of nickel allergy, and has excellent continuous castability and casting quality.  
     The composition of the alloy for slide fasteners is represented by the general formula Cu a Zn b Mn c , wherein regarding a, b and c, in mass %, 10≦b≦20, 8≦c≦15, and a is a remainder, with unavoidable impurities being contained. Moreover, the structure of the alloy is preferably made to be a single α phase at room temperature, and the surface of the alloy is plated.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a copper alloy for slidefasteners, which is used for slide fastener constituent members such asslide fastener elements and stops. More specifically, the presentinvention relates to a copper alloy for slide fasteners having excellentcontinuous castability and casting quality.

[0003] 2. Description of the Prior Art

[0004] Hitherto, as copper alloys for slide fasteners as mentionedabove, for example, copper-nickel-zinc alloys such as nickel silver,which has a white alloy color tone, copper-zinc alloys such as red brassand brass, and so on have been used. Nickel silver contains nickel as analloying element, and thus has excellent corrosion resistance. But, ifit used for a slide fastener or the like, then the problem of nickelallergy may arise because the fastener will often come into contact withthe skin. Moreover, copper-zinc alloys such as red brass and brass donot contain nickel and hence the problem of nickel allergy does notarise, but the color tone thereof is yellowish, and hence a white alloycannot be obtained.

[0005] To solve the above problems, the present applicants thusdeveloped and filed patent applications for nickel-free white copperalloys as disclosed in Japanese Patent Publication Nos. 11-124644,2000303129, 2000-303130 and 2001-3125. The nickel-free white copperalloys disclosed in the above Patent Publications are Cu—Zn—Mn typealloys that have been made to contain Al, Sn or the like; they haveexcellent strength, hardness, workability and corrosion resistance, anddo not contain nickel, and hence the problem of nickel allergy does notarise. Moreover, external appearance of the alloys maintains anattractive degree of whiteness, and hence the alloys are highly valuablefor ornaments.

[0006] An attachment having constituent members such as a slide fasteneris manufactured by following steps: manufacturing wires throughcontinuous casting of the above-described alloy at the start; making thecross-sectional shape of each wire into a prescribed cross-sectionalshape; cutting the wires into the individual constituent members; andthen mounting the constituent members obtained onto an attachment.

[0007] However, the alloys disclosed in the above-mentioned patentpublications do not have as good a continuous castability as thepreviously mentioned nickel silver, red brass and brass, and hence thewire is prone to break during the continuous casting process. Suchbreaking leads to a drop in productivity, and thus causes an increase incost. Moreover, the wires manufactured through the continuous castingmay have portions where die components are attached thereto. Thematerial properties of such portions are different from those of theother portions, and this is not good from the perspective of castingquality.

SUMMARY OF THE INVENTION

[0008] In view of the problems described above, an object of the presentinvention is to provide a copper alloy for slide fasteners which hasexcellent whiteness, does not have the problem of nickel allergy, andhas excellent continuous castability and casting quality.

[0009] The present inventors assiduously studied toward solving theabove problems, and resulted in the following findings.

[0010] 1) Breakage of the wire during the continuous casting processoccurs due to the compounds formed in a die. The compound acts as aresistance to casting, whereupon the wire becomes prone to breaking.

[0011] 2) Dropping of the quality of the continuously cast wire is dueto the compounds, formed in a die, becoming attached to the wiresurface.

[0012] 3) The compounds formed in a die cause the cooling efficiency ofthe alloy to drop and thus internal defects in the alloy to arise. Thedefects deteriorate the properties of the alloy.

[0013] 4) The compounds formed in the die are formed by combiningreadily oxidizable elements that are components of the alloy such as Al,Sn, Ti, Si and Cr with die components.

[0014] Based on these findings, the present inventors discovered that ifreadily oxidizable elements such as Al, Sn, Ti, Si and Cr are not addedas alloy components, then an alloy can be manufactured for which thereis no change in the continuous castability or the casting surface of acast article and there is no local change in properties, because suchelements adversely affect on the continuous castability of the alloy andcause a drop in the casting quality. The present inventors thus attainedthe invention of the present application grounded on the discoveries.

[0015] Specifically, the present invention is constituted as follows.

[0016] (1) A copper alloy for slide fasteners having excellentcontinuous castability, having a composition represented by a generalformula Cu_(a)Zn_(b)Mn_(c), wherein regarding a, b and c, in mass %,10≦b≦20, 8≦c≦15, and a is a remainder, with unavoidable impurities beingcontained.

[0017] (2) A copper alloy for slide fasteners according to (1) above,wherein a color tone is such that a* and b*, which represent a colortone as stipulated in JIS Z 8729, satisfy 0<a*<2 and 7<b*<16.

[0018] (3) A copper alloy for slide fasteners according to (1) or (2)above, being a single α phase at room temperature.

[0019] (4) A copper alloy for slide fasteners according to any of (1)through (3) above, wherein a surface of the copper alloy is plated.

[0020] (5) An element being a constituent member of a slide fastener,comprising the copper alloy for slide fasteners according to any of (1)through (4).

[0021] (6) A stop being a constituent member of a slide fastener,comprising the copper alloy for slide fasteners according to any of (1)through (4).

[0022] Following is a description of the copper alloy for slidefasteners of the present invention.

[0023] With the copper alloy for slide fasteners of the presentinvention, the object of the present invention can be attained by makingthe alloy be a composition represented by the following general formula:

Cu_(a)Zn_(b)Mn_(c)  (1)

[0024] wherein, regarding a, b and c, in mass %, 10≦b≦20, 8≦c≦15, and ais a remainder, with unavoidable impurities being contained.

[0025] The element Zn, which is a component of the alloy of the presentinvention, has an effect of improving the mechanical properties and thework-hardening properties of the alloy through solid solutionstrengthening, a deoxidation effect during melt casting, and an effectof reducing the cost of the alloy. If the Zn proportion is below thenumerical range defined above, then the reduction in the cost of thealloy will be insufficient, the strength of the alloy will decrease, andthe castablility will worsen, because the melt will become prone tooxidation and hence oxides will grow in the alloy. On the other hand, ifthe Zn proportion is above the numerical range stipulated above, thenthe crystalline structure will become α+β, and hence the alloy will nolonger exhibit sufficient cold workability.

[0026] The proportion b of Zn is preferably such that 10<b<20, morepreferably such that 13<b<17.

[0027] The element Mn, which is another component of the alloy of thepresent invention, has an effect of improving the mechanical propertiesof the alloy through solid solution strengthening, and an effect ofreducing the cost of the alloy. By adding Mn instead of Zn, the seasoncracking resistance is improved, and the color tone of the copper alloyis prevented from becoming too yellow. Mn reduces the melting point ofthe alloy, and hence Mn acts to improve the castability and alsosuppress vaporization of zinc from the melt. If the Mn proportion isbelow the numerical range stipulated above, the color tone will becomeyellowish. Whereas, if the Mn proportion is above the same range, oxideswill increase during melt casting and hence the castability will worsen,and the crystalline structure will become α+β, thereby, the alloy willno longer keep sufficient cold workability and the castability willworsen.

[0028] The proportion c of Mn is preferably such that 8<c<14, morepreferably such that 8<c<12.

[0029] In the present invention, it is important that readily oxidizableelements such as Al, Sn, Ti, Si and Cr are not added, because theseelements damage the continuous castability and cause a drop in thecasting quality.

[0030] The alloy of the present invention displays the color in rangesof 0<a*<2 and 7<b*<16 based on the chromaticity diagram of the L*, a*,b* color system stipulated in JIS Z 8729. Note that the ‘color tone’mentioned in the present specification is expressed using the method forindicating the color of objects stipulated in JIS Z 8729, and isrepresented by the values of the lightness index L* (lightness: L star)and the chromaticity indexes a* (greenness to redness: a star) and b*(blueness to yellowness: b star).

[0031] By making the structure of the alloy of the present invention bea single α phase, an alloy having improved cold workability can beprovided. Furthermore, by plating the surface of the alloy, an alloyhaving excellent corrosion resistance and discoloration resistance canbe provided.

[0032] Following is a detailed description, with reference to thedrawings, of a slide fastener, which is a usage of the alloy of thepresent invention.

[0033]FIG. 1 is a conceptual drawing of a slide fastener. As shown inFIG. 1, the slide fastener comprises a pair of fastener tapes 1 each ofwhich has a core part 2 formed at a side edge thereof, elements 3 thatare crimped (mounted) onto the core part 2 of each fastener tape 1 at aprescribed interval, a top stop 4 and a bottom stop 5 that are crimpedonto the core part 2 of each fastener tape 1 at the top and bottom endsrespectively of the elements 3, and a slider 6 that is disposed betweenfacing pairs of elements 3 and can be freely slid in an up/downdirection to engage or separate the elements 3. In the above, a slidefastener chain 7 is an article obtained by mounting elements 3 onto thecore part 2 of a fastener tape 1.

[0034] Although not shown in the drawings, slider 6 as shown in FIG. 1is manufactured by the following steps: pressing a long plate-shapedbody having a rectangular cross section, through several stages; cuttingthe body at a prescribed interval to form slider bodies; and thenmounting a spring or pull on the slider body if necessary. The pulls arealso manufactured from the plate-shaped body having a rectangular crosssection, by punching out into a prescribed shape, and are crimped ontothe slider bodies. The bottom stop 5 may be a separable fittingcomprising an insert pin, a box pin and a box, so that the pair of slidefastener chains can be separated through the opening by the slider.

[0035]FIG. 2 shows a method of manufacturing the elements 3, the topstops 4 and the bottom stops 5 of the slide fastener shown in FIG. 1,and a method of attaching these to the core parts 2 of the fastenertapes 1. As shown in the drawing, the elements 3 are prepared by thebelow steps: a deformed wire 8 having an approximately Y-shaped crosssection is cut into pieces of a prescribed dimension; and pressing thepieces to form an engaging head part 9 on each element 3. And then, footparts 10 of each element 3 are crimped onto the core part 2 of thefastener tape 1, and thus mounting on the element 3.

[0036] The top stop 4 is prepared by cutting a rectangular wire 11having a rectangular cross section into pieces of a prescribeddimension, bending the pieces to have an approximately C-shaped crosssection. And then, the top stop 4 is crimped onto the core part 2 of thefastener tape 1, thus mounting on the top stop 4. The bottom stop 5 isprepared by cutting the deformed wire 12 having an approximatelyX-shaped cross section into pieces of a prescribed dimension. And then,the top stop 5 is crimped onto the core part 2 of the fastener tape 1,thus mounting on the top stop 5.

[0037] Note that in the drawing, it appears that the elements 3 and thetop and bottom stops 4 and 5 are mounted onto the fastener tape 1 at thesame time. But, in actual practice, elements 3 are first attachedcontinuously onto the fastener tape 1 to compose a fastener chain, andthen the elements 3 in regions where a stop is to be attached areremoved from the fastener chain. And, the prescribed stops 4 and 5 aremounted on in these regions near to the elements 3.

[0038] In order to manufacture and attach the constituent members asdescribed above, it is necessary for the elements and the stops to makeup the constituent members of the slide fastener to be an alloy havingexcellent cold workability.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039]FIG. 1 is a conceptual drawing of a slide fastener.

[0040]FIG. 2 is a drawing to explain a method of attaching a bottomstop, a top stop and elements to a fastener tape.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] Following is a specific description of the present inventionthrough an example and a comparative example. However, the presentinvention is not limited whatsoever by the following example.

EXAMPLE

[0042] Using (99.99%) pure Cu, (99.9%) pure Zn and (99.9%) pure Mn asraw materials, these materials were melted in a continuous castingapparatus such that the composition would become Cu₇₅Zn₁₅Mn₁₀ by mass %,and continuous wires were manufactured by casting the melt through acarbon die of diameter 8 mm.

Comparative Example

[0043] Continuous wires were manufactured by the same method as in theExample, except that the composition was made to be Cu₈₃Zn₄Mn₁₂Al₁ bymass %.

[0044] The continuous wires obtained through the above Example andComparative Example were evaluated with regard to continuouscastability, surface state and so on.

[0045] The continuous castability of the alloys was evaluated by severaltimes of actual continuous casting using the above-mentioned continuouscasting apparatus. With the alloy of the Comparative Example, the wirebroke when the weight thereof was between 100 and 150 kg, whereas withthe alloy of the Example, the wire broke when the weight thereof wasbetween 300 and 500 kg. It was thus found that the continuouscastability was 2 to 5 times better for the alloy of the Example of thepresent invention than that of the Comparative Example.

[0046] Moreover, the surface of each wire manufactured was observed,some parts blackened near the broken point with several continuous wiresof the Comparative Example. On the other hand, with wires of theExample, such blackened portions were not present. Upon analyzing theblackened portions, it was found that they were a compound of Al and thecarbon of the die. Upon cutting the wires just at the blackened part andobserving the cut surface, internal defects such as cavities were found.Moreover, upon observing the structure of the continuous wire of thepresent invention, it was found that the structure was a single α phase.

[0047] The continuous wires of the Example were subjected to drawing androlling, thus manufacturing continuous deformed wires respectivelyhaving an approximately Y-shaped cross section and an approximatelyX-shaped cross section, and a continuous rectangular wire, as shown inFIG. 2. Next, the continuous deformed wires and the continuousrectangular wire obtained were subjected to several cold workings toform every constituent member. And, the constituent members were mountedon fastener tapes, thus manufacturing a slide fastener. The slidefastener manufactured did not contain nickel and hence there would be nonickel allergy. Furthermore, the external appearance displays excellentwhiteness as with a slide fastener manufactured based on nickel silver,and the color was within the above-mentioned ranges for a* and b*stipulated in JIS Z 8729. Moreover, during the manufacture of the slidefastener, cold working was easily performed, with no problem inworkability.

[0048] Furthermore, during a slide fastener was manufactured asdescribed above, after forming the continuous deformed wires and thecontinuous rectangular wire, the wires were electrolytically plated witha Cu—Sn alloy. And then, after mounting the constituent members on thefastener tapes, the slide fastener was electroless-plated with Sn.Except for the additional plating processes, the slide fastener wasmanufactured in the same way as described above.

[0049] The slide fastener obtained was as good as described earlier withregard to all of nickel allergy, whiteness and workability. Moreover,upon investigating the corrosion resistance and the discolorationresistance, it was found that the effects were more prominent than withthe slide fastener unaccompanied the plating described earlier.

[0050] According to the present invention, a copper alloy for slidefasteners having the following advantages can be provided: The alloydisplays excellent whiteness, does not contain nickel and hence does nothave the problem of nickel allergy, and has excellent continuouscastability and casting quality.

What is claimed is:
 1. A copper alloy for slide fasteners havingexcellent continuous castability, having a composition represented by ageneral formula Cu_(a)Zn_(b)Mn_(c), wherein regarding a, b and c, inmass %, 10≦b≦20, 8≦c≦15, and a is a remainder, with unavoidableimpurities being contained.
 2. A copper alloy for slide fastenersaccording to claim 1, wherein a color tone such that a* and b*, whichrepresent a color tone as stipulated in JIS Z 8729, satisfy 0<a*<2 and7<b*<16.
 3. A copper alloy for slide fasteners according to claim 1,being a single α phase at room temperature.
 4. A copper alloy for slidefasteners according to claim 1, a surface thereof being plated.
 5. Anelement, which is a constituent member of a slide fastener, comprisingthe copper alloy for slide fasteners according to claim
 1. 6. A stop,which is a constituent member of a slide fastener, comprising the copperalloy for slide fasteners according to claim 1.